Vehicle suspension with lift axle and pivotal lift spring

ABSTRACT

A lift axle suspension system for use on a vehicle having a chassis. The lift axle suspension system includes an axle assembly that is operably coupled to the vehicle chassis with a support arm assembly. A support biasing member is located between the axle assembly and the vehicle chassis for transferring loads between the axle assembly and the vehicle chassis. A lift spring member is also provided. The lift spring member is an air spring member and has one end that is pivotally mounted. Extension of the lift spring member lifts the axle assembly from a use position where the wheels attached to the axle assembly are engageable with a road surface to a storage position where the wheels attached to the axle assembly are not engaged with the road surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to lift axle suspension systems and, moreparticularly, to a lift axle suspension system having an air spring liftmember.

2. Description of the Related Art

A variety of lift axle suspension systems are known in the art. Manyheavy-duty trucks and similar vehicles utilize one or more liftableauxiliary axles also referred to as lift axles. When the truck iscarrying a heavy load, the lift axle will be lowered so that the wheelsmounted on the lift axle can engage the road surface and the lift axlecan bear a portion of the vehicle load. The axle is lifted out ofservice, with its wheels disengaged from the road surface, when thetruck is empty or carrying only a light load and the additional loadcarrying capacity provided by the lift axle assembly is not required.

Such lift axles often employ two identical parallelogram linkageslocated on opposite sides of the vehicle. Each of the parallelogramlinkages includes an upper support arm and a lower support arm.Typically, the upper and lower support arms are pivotally mounted on asupport hanger that extends downwardly from a longitudinal rail memberof the truck chassis on one end and pivotally connected to the lift axleon their opposite ends. A support spring, typically an air spring, isprovided between the axle assembly and the chassis to transfer loadsbetween the truck chassis and the axle assembly when the axle is loweredand the attached wheels engage the road surface. A second air spring isconventionally used to provide a lift spring for the axle assembly. Suchlift axles may also be steerable axles and include steering mechanisms.

When it is desired to lower the lift axle, the support air springpositioned between the axle assembly and chassis is energized orinflated to extend the support spring and the lift air spring issimultaneously de-energized or deflated to retract the lift spring. Toraise the lift axle, the support air spring is de-energized or deflatedto retract the support spring and the lift air spring member isenergized or inflated to extend the lift spring. Known lift axlesuspensions have employed lift spring members in a number of differentpositions for lifting the axle assembly. While such known assemblies areeffective, an improved lift axle suspension system that is rugged,reliable and that can be cost effectively manufactured is desirable.

SUMMARY OF THE INVENTION

The present invention provides a lift axle suspension system having alift spring that is pivotally mounted at one end and which can bepivotally mounted to a cross member extending between hangers on thevehicle chassis.

The invention comprises, in one form thereof, a suspension system thatincludes a vehicle chassis, an axle assembly and a support arm assemblyoperably coupling the axle assembly to the vehicle chassis wherein theaxle assembly is vertically moveable relative to the vehicle chassis. Asupport biasing member, such as an air spring, is disposed between theaxle assembly and the vehicle chassis. A lift spring member is alsoprovided. The lift spring member is an air spring with opposing firstand second ends and defines a central axis. Each of the first and secondlift spring ends are operably coupled to the suspension system whereinextension of the lift spring vertically displaces the axle assemblyrelative to the vehicle chassis. The first lift spring end is pivotallymounted about a pivot axis wherein the central axis of the lift springintersects the pivot axis.

The invention comprises, in another form thereof, a lift axle suspensionassembly for a vehicle having a chassis. The lift axle suspensionassembly includes an axle assembly and a pair of support arms operablycoupling the axle assembly to the vehicle chassis wherein the axleassembly is moveable relative to the vehicle chassis between a storageposition and a use position. A support biasing member is operablydisposed between the axle assembly and the vehicle chassis. A liftspring member is also provided. The lift spring member is an air springthat defines a central axis and has opposing first and second ends. Thelift spring member is operably disposed between the axle assembly andthe vehicle chassis wherein extension of the lift spring member movesthe axle assembly from the use position to the storage position. Thefirst lift spring end is pivotal about a pivot axis and the central axisof the lift spring member intersects the pivot axis.

The invention comprises, in yet another form thereof, a suspensionsystem that includes a vehicle chassis and an axle assembly. The vehiclechassis has first and second longitudinal members with first and secondhangers respectively extending downwardly from the first and secondlongitudinal members. A cross member extends between the two hangers. Asupport arm assembly operably couples the axle assembly to the vehiclechassis wherein the axle assembly is vertically moveable relative to thevehicle chassis. A support biasing member, such as an air spring, isdisposed between the axle assembly and the vehicle chassis. At least onelift spring member is also provided. The lift spring member is an airspring with opposing first and second lift spring ends. The first liftspring end is pivotally mounted to the cross member and the second liftspring end is coupled to the support arm assembly wherein extension ofthe lift spring member vertically displaces the axle assembly.

The invention comprises, in still another form thereof, a lift axlesuspension assembly for a vehicle having a chassis. The lift axlesuspension assembly includes an axle assembly and a support arm assemblyoperably coupling the axle assembly to the vehicle chassis wherein theaxle assembly is vertically moveable relative to the vehicle chassisbetween an uppermost position and a lowermost position. A supportbiasing member is operably disposed between the axle assembly and thevehicle chassis. A lift spring member is also provided. The lift springmember is an air spring and has opposing first and second ends anddefines a central axis. The first end of the lift spring member ispivotally mounted about a pivot axis. The lift spring member is operablydisposed between the vehicle chassis and the axle assembly whereinextension of the lift spring member vertically displaces the axleassembly. The central axis has a first angular position relative to thepivot axis when said axle assembly is in the lowermost position and asecond angular position relative to the pivot axis when the axleassembly is in the uppermost position. The first and second angularpositions of the lift spring member define a first predefined angularrange therebetween. First and second pivot stops are disposed proximatethe first end of the lift spring member wherein the first pivot stoplimits rotation of the lift spring member in a first rotationaldirection about the pivot axis and the second pivot stop limits rotationof the lift spring member in a second opposite rotational directionabout the pivot axis whereby rotation of the lift spring member aboutthe pivot axis is limited to a second predefined angular range. Thesecond predefined angular range being larger than the first predefinedangular range.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features of this invention, and the mannerof attaining them, will become more apparent and the invention itselfwill be better understood by reference to the following description ofan embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is an exploded perspective view of a lift axle suspension systemin accordance with the present invention.

FIG. 2 is a perspective view of the lift axle suspension system.

FIG. 3 is a top view of the lift axle suspension system.

FIG. 4 is another perspective view of the lift axle suspension system.

FIG. 5 is a partial perspective view of the lift axle suspension system.

FIG. 6 is a side view of the lift axle suspension system in an uppermoststorage position.

FIG. 7 is a side view of the lift axle suspension system in a useposition.

FIG. 8 is a side view of the lift axle suspension system in a lowermostposition.

FIG. 9 is a perspective view of a structural member having a sleeve andpivot bushing.

FIG. 10 is a perspective view of cross member with structural membersfor pivotally supporting two lift spring members.

FIG. 11 is a front view of the cross member and structural members ofFIG. 10.

FIG. 12 is a side view of the cross member and structural members ofFIG. 10.

FIG. 13 is a side view of a pivot mount that is secured to the liftspring member.

FIG. 14 is an end view of the pivot mount of FIG. 13.

FIG. 15 is a plan view of the pivot mount of FIG. 13.

FIG. 16 is a top view of an upper support arm of the suspension systemof FIG. 1.

FIG. 17 is a side view of the upper support arm of FIG. 16.

FIG. 18 is an end view of the upper support arm of FIG. 16.

FIG. 19 is a schematic representation of the rotational movement of liftspring member.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the exemplification set outherein illustrates an embodiment of the invention, in one form, theembodiment disclosed below is not intended to be exhaustive or to beconstrued as limiting the scope of the invention to the precise formdisclosed.

DETAILED DESCRIPTION OF THE INVENTION

A lift axle suspension system 20 in accordance with the presentinvention is shown in an exploded view in FIG. 1. Suspension system 20is shown in a deployed or in use position in FIGS. 2-4 and includes anaxle assembly 22 that is attached to vehicle chassis 24 with support armassemblies 26.

Vehicle chassis 24 includes two structural rails 28 that extendlongitudinally along the vehicle and form a portion of the vehicleframe. The frames of heavy duty vehicles typically include twostructural rails that are located on opposite sides of the vehicle andthat extend for the longitudinal length of the truck bed or payload areaof the vehicle. One or both of the longitudinal members or rails 28 areomitted from many of the Figures for purposes of graphical clarity.Vehicle chassis 24 also includes two support hangers 30 which extenddownwardly from the two longitudinal rails 28. A cross member 32 extendslaterally between the two support hangers 30 and also forms a portion ofchassis 24.

Two support arm assemblies 26 are used to mount axle assembly 22 to thevehicle chassis 24 with each of the support arm assemblies 26 beingsecured to a respective one of the support hangers 30. Each of thesupport arm assemblies 26 includes an upper support arm 34 and a lowersupport arm 36. At one end, the upper and lower support arm 34, 36 ofeach assembly 26 is pivotally attached to a support hanger 30. Theopposite ends of the upper and lower support arms 34, 36 are pivotallyattached to the axle assembly 22 through a saddle member 38. Nut andbolt assemblies 40 are used to pivotally secure the upper and lowersupport arms 34, 36 which include a pivot sleeve 42 having a pivotbushing located therein at each of their ends for receiving boltassemblies 40.

The upper and lower support arms 34, 36 are mounted to define aparallelogram linkage so that the caster angle of axle assembly 22remains substantially constant as the axle assembly is raised andlowered with respect longitudinal rails 28. The use of upper and lowersupport arms in a parallelogram linkage assembly to attach an axleassembly to a vehicle chassis is well known to those having ordinaryskill in the art. Gideon et al. in U.S. Pat. No. 6,158,750 disclose oneexample of a lift axle suspension having upper and lower support armsand pivot bearings at the ends of such support arms that can be adaptedfor use with the present invention, the disclosure of which is herebyincorporated herein by reference.

Axle assembly 22 includes an axle 44 attached to saddle members 38.Wheel hubs 46 are attached at the opposite ends of axle 44 for attachingwheels (not shown). Axle assembly 22 also includes a steering mechanism48 proximate each wheel hub 46 for controlling the steering angle of thewheel hubs 46 and attached wheels in a manner well known to those havingordinary skill in the art. Although axle assembly 22 illustrates oneexample of an axle assembly that can be used with the present invention,alternative axle assemblies, e.g., an axle assembly without steeringmechanisms, can also be employed with the present invention.

Support biasing members 50 are positioned between axle assembly 22 andthe vehicle chassis 24 to transfer loads between the chassis 24 and axleassembly 22. Two air spring suspension springs are used to form thesupport biasing members 50 in the illustrated embodiment. Air springs 50have a bottom plate 52 secured to horizontal mounting sections 54 ofsaddle members 38 to thereby couple the air springs 50 with axle 44.Each of the air springs 50 also has an upper plate 56 that is secured toone of the longitudinal rails 28 through mounting member 58. When airsprings 50 are inflated and axle 44 is positioned so that wheelsattached thereto will engage the road surface, air springs 50 functionas suspension springs transferring a portion of the weight of thevehicle to axle assembly 22 where it is subsequently transferred to theroad surface by the attached wheels.

A lift spring member 60 is secured between each of the upper supportarms 34 and cross member 32 and is used to vertically displace axleassembly 22. More specifically, inflation of lift spring member 60,occurring contemporaneously with the deflation of air springs 50, liftsthe wheels attached to axle assembly 22 out of engagement with the roadsurface when the vehicle does not require the extra load carryingcapacity provided by axle assembly 22. Lift spring member 60 is an airspring. Double convoluted and triple convoluted air springs suitable forair springs 60 and 50 respectively, are commercially available fromFirestone Industrial Products Company having a place of business atCarmel, Ind.

For each of the support arm assemblies 26, lift spring 60 has a fixedend 62 that is non-pivotally secured to a rigid member 64 that extendsfrom upper support arm 34 laterally inwardly toward the longitudinalcenter line of the vehicle located midway between rails 28 anddownwardly. The configuration of upper support arms 34 is best seen inFIGS. 16-18. Rigid member 64 includes openings 65 for receiving boltshafts (not shown) extending from spring end 62 to rigidly fix springend 62 to upper support arm 34. The opposite end 66 of lift spring 60 ispivotally mounted.

Attached to end 66 of each of lift springs 60 is a pivot mount 68 whichis separately illustrated in FIGS. 13-15. As best seen in FIG. 14, pivotmount 68 has a generally U-shaped configuration with a central web 70and two sidewalls 72. Aligned openings 74 are provided in sidewalls 72for receiving a bolt which acts as pivot pin 76 and defines a pivot axis78 about which lift spring 60 is pivotal. Openings 73 in central web 70receive bolt shafts for securing pivot mount 68 to an end 66 of a liftspring 60. A structural member 80 is secured to cross member 32 and hasa generally I-shaped cross section with upper and lower horizontalflanges 79, 81, and a vertical web 83. A metal sleeve 84 extendstransversely to structural member 80 and is secured at the distal end 82of member 80. A bushing 86 is located in sleeve 84 for rotationalengagement with pivot pin 76. Structural members 80 can be welded tocross member 32 or have mounting flanges which allow members 80 to bebolted to cross member 32. FIG. 5 provides a partial perspective view oflift axle suspension system 20 that illustrates one of longitudinalrails 28, hangers 30, cross member 32, structural members 80 (only oneis visible in FIG. 5), lift springs 60 and upper support arms 34.

Two pivot stops 88, 90 are also mounted on structural member 80. Theupper pivot stop 88 is located vertically above pivot axis 78 and thelower pivot stop 90 is located below pivot axis 78. Pivot stops 88, 90are steel plate and lie in a plane oriented perpendicular to pivot axis78 and are positioned parallel and midway between sidewalls 72 wherebypivot stops 88, 90 are engageable with central web 70 to limit therotation of lift spring 60. More specifically, when lift spring 60 isrotated upwardly about pivot axis 78, upper pivot stop 88 defines alimit to the angular range within which lift spring 60 can be rotatedand, when lift spring 60 is rotated downardly about pivot axis 78, lowerpivot stop 90 defines a limit to the angular range within which liftspring 60 can be rotated.

The operation of lift axle suspension system 20 is best understood withreference to the side views of system 20 presented in FIGS. 6-8 whichillustrate the vertical movement of axle assembly 22 relative to vehiclechassis 24. FIG. 6 illustrates system 20 wherein support spring 50 isdeflated and compressed and lift spring 60 has been inflated andextended to thereby place axle assembly 22 in its uppermost positionrelative to vehicle chassis 24. This uppermost position of axle assembly22 shown in FIG. 6 defines a storage position for axle assembly 22. Whenaxle assembly 22 is placed in the storage position of FIG. 6, the wheelsattached to axle assembly 22 will be lifted off the road surface andaxle assembly 22 will not bear any of the weight of the vehicle.

FIG. 7 illustrates system 20 wherein support spring 50 has been inflatedand extended and lift spring 60 has been deflated and compressed tothereby lower axle assembly 22 into a use position. In this use positionof FIG. 7, the wheels attached to axle assembly 22 will be engaged withthe road surface and loads will be transferred to the road surface fromrails 28 through support springs 50 and axle assembly 22. As will beappreciated by those having ordinary skill in the art, suspension system20 is designed to allow for a range of vertical movement of each of thetwo opposite ends of axle assembly 22 and the wheels attached theretowhile still transferring loads to axle assembly 22 through supportsprings 50 to facilitate travel over uneven road surfaces. Thus, duringnormal use, axle assembly 22 may move slightly upwardly and downwardlyfrom the use position shown in FIG. 7 with support springs 50transferring loads between axle assembly 22 and longitudinal rails 28.FIG. 8 illustrates support spring 50 in its fully extended position andthe lower limit or lowermost position of axle assembly 22 when the axleassembly 22 has been lowered to bear a portion of the vehicle load.

When it is desired to once again raise axle assembly 22 to its storageposition, the support springs 50 are deflated and lift springs 60 areinflated to thereby extend springs 60 and raise axle assembly 22 to theposition shown in FIG. 6. As lift springs 60 are inflated and extended,pivotal ends 66 of lift springs 60 pivot about pivot axes 78 while theopposite ends 62 of lift springs 60 which are fixed relative to uppersupport arms 34 bias support arm assemblies 26 and attached axleassembly 22 upwardly to their storage positions. Although a particularlocation for lift spring members 60 is illustrated in the attacheddrawings, alternative attachment locations are also possible for liftspring members 60. For example, instead of fixing lift spring ends 62relative to upper support arms 34, lift spring ends 62 could be attachedto axle assembly 22 through saddle members 38. Those having ordinaryskill in the art will recognize that other modifications are alsopossible within the scope of the present invention.

Lift springs 60 have rigid plates 62 a, 66 a located respectively atopposite ends 62, 66. Lift springs 60 also define a central axis 61.Central axis 61 intersects the pivot axis 78. When the plates 62 a, 66 aat ends 62, 66 are positioned parallel to each other, the central axis61 of that spring 60 extends linearly along the centerline of the liftspring 60 and intersects rigid plates 62 a, 66 a at equal, substantiallyperpendicular angles. As can be seen in FIGS. 6-8, as axle assembly 22moves vertically, each lift spring 60 pivots about pivot axis 78 todefine different angular positions for the central axis 61 of the liftsprings 60.

When lift springs 60 are first inflated to initiate the upward movementof axle assembly 22 towards its storage position, lift springs 60 arelikely to bulge transversely relative to central axis 61 and causingpivotal motion about pivot axis 78. Excessive rotation about pivot axis78 could damage lift springs 60, however, limited rotation about pivotaxis 78 is not necessarily damaging and could even be desirable inlimited circumstances to relieve stresses on some of the components ofsystem 20. FIG. 19 provides a schematic representation of the rotationalmovement of central axis 61 of a lift spring 60. It is noted that theangles presented in this Figure are not necessarily to scale and arepresented for purposes of graphical clarity in understanding theoperation of system 20.

In FIG. 19, line 61 a represents the angular position of central axis 61when axle assembly 22 is in its uppermost position depicted in FIG. 6,line 61 b represents the angular position of central axis 61 when axleassembly 22 is in its lowermost position depicted in FIG. 8 and line 61c represents the angular position of central axis 61 when axle assembly22 is in the use position depicted in FIG. 7. Line 61 d represents theupper boundary of central axis 61 during normal use of axle assembly 22.In other words, when axle assembly 22 is lowered to engage the wheelsattached thereto with the road surface, the normal vertical range ofmotion for axle assembly 22, and concomitant rotation of central axis61, is represented by angular range 92. Angular range 94 represents thepredefined angular range of movement for central axis 61 between thelowermost position of axle assembly 22 depicted in FIG. 8 and theuppermost position of axle assembly 22 depicted in FIG. 6. For each ofthe lines 61 a, 61 b, 61 c and 61 d, the position of these lines assumethat lift spring 60 and central axis defined thereby are in a linearconfiguration with the rigid plates 62 a, 66 a located on opposite ends62, 66 of lift spring 60 being position parallel to one another.

Also depicted in FIG. 19 are lines 89 and 91 which are the outer limitsof another predefined angular range 96. Line 89 corresponds to thelocation of central axis 61 if lift spring 60 were to be rotatedupwardly until its further rotation was prevented by pivot stop 88.Similarly, line 91 corresponds to the location of central axis 61 iflift spring 60 were to be rotated downwardly until its further rotationwas prevented by pivot stop 90. As discussed above, axle assembly 22does not travel upwardly beyond the point depicted in FIG. 6 ordownwardly below the point depicted in FIG. 8, however, the central axis61 of lift springs 60 are not always linear in shape. More specifically,when axle assembly 22 is in its uppermost position, it is possible forrigid plate 66 a and attached pivot mount 68 to rotate further upwardlycausing a bend in air spring 60. Pivot stop 88 limits this furtherupward rotational travel of plate 66 a and pivot mount 68 to the angularlocation depicted by line 89. With regard to this line 89, it is notedthat at pivotal end 66, central axis 61 is considered to intersect rigidplate 66 a at a perpendicular angle and it is this central axis thatcannot rotate beyond line 89. Similarly, when axle assembly 22 is in itslowermost position, pivot stop 90 limits the rotation of pivot mount 68and attached rigid plate 66 a, and central axis 61 defined thereby, tothe position indicated by line 91.

When lift spring 60 is in its fully inflated condition, as in FIG. 6,lift spring 60 will naturally seek to be in a linear configuration withend plates 62 a and 66 a being positioned parallel with each other andcentral axis in the position depicted by line 61 a. It is possible forstop 88 to be located to prevent any further upward rotation of pivotalend 66 of lift spring 60 at this location. In other words, it ispossible to configure pivot stop 88 so that line 89 is collinear withline 61 a, however, if pivot stop 88 is misaligned it could prevent liftspring 60 from rotating completely upwards to the angular positionindicated by line 61 a. By positioning pivot stop 88 to permit theslight overration of pivotal end 66, the manufacture and assembly ofsystem 20 and the locating of pivot stop 88 is facilitated. Similarly,pivot stop 90 is positioned to allow a slight overrotation of pivotalend 66. The magnitude of this overrotation, e.g., the angular distancebetween lines 89 and 61 a and between lines 61 b and 91 is limited toprevent damage to lift spring 60. Generally, air spring manufacturersestablish limits on such angular deviation and allowing an angulardeviation greater than the manufacturer's limit will void the warrantyprovided with the air spring. The angular distance between lines 89 and61 a and between lines 61 b and 91 is preferably selected to remainwithin the air spring manufacturer's guidelines.

It is noted that in the illustrated embodiment both lines 89 and 91 lieoutside the angular range 94 defined by lines 61 a and 61 b to define alarger angular range 96. Stops 88, 90 can, however, also be positionedto define an angular range 96 that is larger than angular range 94 bypositioning the stops 88, 90 such that line 89 and line 61 a arecollinear and only line 91 lies outside angular range 94, or, bypositioning stops 88, 90 such that line 91 and line 61 b are collinearand only line 89 lies outside angular range 94. In still otherembodiments, pivotal stops 88, 90 could be positioned such that lines 89and 91 are collinear with lines 61 a and 61 b respectively and angularranges 94 and 96 are substantially equal.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles.

1. A suspension system comprising: a vehicle chassis; an axle assembly;a support arm assembly operably coupling said axle assembly to saidvehicle chassis wherein said axle assembly is vertically moveablerelative to said vehicle chassis; a support biasing member operablydisposed between said axle assembly and said vehicle chassis; and a liftspring member wherein: (a) said lift spring member is an air spring thatdefines a central axis and has opposing first and second ends; (b) eachof said first and second lift spring ends are operably coupled to saidsuspension system wherein extension of said lift spring membervertically displaces said axle assembly relative to said vehiclechassis; and (c) said first lift spring end is pivotally mounted about apivot axis and wherein said central axis intersects said pivot axis. 2.The suspension system of claim 1 wherein said central axis intersectssaid pivot axis at an angle of approximately 90 degrees.
 3. Thesuspension system of claim 1 further comprising a first pivot stop and asecond pivot stop, said first and second pivot stops being operablycoupled with said first lift spring end and limiting rotation of saidfirst lift spring end about said pivot axis to a predefined angularrange.
 4. The suspension system of claim 1 wherein said pivot axis isfixed relative to said vehicle chassis.
 5. The suspension system ofclaim 1 wherein said second lift spring end is non-pivotally fixedrelative to a portion of said support arm assembly.
 6. The suspensionsystem of claim 1 wherein said vehicle chassis comprises first andsecond downwardly extending hangers and a cross member extending betweensaid hangers; wherein said suspension system further comprises a secondsupport arm assembly vertically coupling said axle assembly to saidvehicle chassis, said support arm assembly being coupled to said firsthanger and said second support arm assembly being coupled to said secondhanger; and wherein said first lift spring end is pivotally mounted onsaid cross member.
 7. The suspension system of claim 6 furthercomprising a second lift spring member, said second lift spring memberbeing an air spring defining a second central axis, said second liftspring member having opposing third and fourth lift spring ends, each ofsaid third and fourth lift spring ends being operably coupled to saidsuspension system wherein extension of said second lift springvertically displaces said axle assembly relative to said vehicle chassisand wherein said third lift spring end is pivotally mounted to saidcross member and is pivotal about a second pivot axis, said second pivotaxis and said second central axis intersecting at an angle ofapproximately 90 degrees.
 8. The suspension system of claim 1 furthercomprising a first pivot stop and a second pivot stop, said first pivotstop being fixed relative to said vehicle chassis and limiting pivotalmovement of said lift spring member in a first rotational direction,said second pivot stop being fixed relative to said vehicle chassis andlimiting pivotal movement of said lift spring member in an oppositesecond rotational direction.
 9. The suspension system of claim 8 furthercomprising a pivot mount secured to said first lift spring end, saidpivot mount having a generally U-shaped configuration with a pair ofside walls and a central web extending therebetween, said pivot axisextending between said sidewalls and intersecting said sidewalls at asubstantially perpendicular axis, said first and second pivot stopsbeing engageable with said central web on opposite sides of said pivotaxis to thereby limit rotation of said first lift spring end.
 10. A liftaxle suspension assembly for a vehicle having a chassis, said lift axlesuspension assembly comprising: an axle assembly; a pair of support armsoperably coupling said axle assembly to the vehicle chassis wherein saidaxle assembly is moveable relative to the vehicle chassis between astorage position and a use position; a support biasing member operablydisposed between said axle assembly and the vehicle chassis; and a liftspring member wherein: (a) said lift spring member is an air spring thatdefines a central axis and has opposing first and second ends; (b) saidlift spring member is operably disposed between said axle assembly andthe vehicle chassis wherein extension of the lift spring member movesthe axle assembly from the use position to the storage position; and (c)said first lift spring end is pivotal about a pivot axis and whereinsaid central axis intersects said pivot axis.
 11. The lift axlesuspension assembly of claim 10 wherein said central axis intersectssaid pivot axis at an angle of approximately 90 degrees.
 12. Thesuspension system of claim 11 further comprising a first pivot stop anda second pivot stop, said first and second pivot stops being operablycoupled with said first lift spring end and limiting rotation of saidfirst lift spring end about said pivot axis to a predefined angularrange.
 13. The suspension system of claim 10 wherein said pivot axis isfixed relative to the vehicle chassis.
 14. The suspension system ofclaim 10 wherein said second lift spring end is non-pivotally fixedrelative to one of said support arms.
 15. The suspension system of claim10 further comprising first and second downwardly extending hangerssecured to the vehicle chassis and a cross member extending between saidhangers; wherein said suspension system further comprises a second pairof support arms operably coupling said axle assembly to the vehiclechassis, said pair of support arms being coupled to said first hangerand said second pair of support arms being coupled to the vehiclechassis through said second hanger; and wherein said first lift springend is pivotally mounted on said cross member.
 16. A suspension systemcomprising: a vehicle chassis including first and second longitudinalmembers, first and second hangers extending downwardly respectively fromsaid first and second longitudinal members and a cross member extendingbetween said first and second hangers; an axle assembly; a support armassembly operably coupling said axle assembly to said vehicle chassiswherein said axle assembly is vertically moveable relative to saidvehicle chassis; a support biasing member operably disposed between saidaxle assembly and said vehicle chassis; and at least one lift springmember, said lift spring member being an air spring, said lift springmember having opposing first and second lift spring ends, said firstlift spring end being pivotally mounted to said cross member, saidsecond lift spring end being coupled to said support arm assemblywherein extension of said lift spring member vertically displaces saidaxle assembly.
 17. The suspension system of claim 16 wherein said airspring defines a central axis and is pivotal about a pivot axis, saidcentral axis and said pivot axis intersecting at an angle ofapproximately 90 degrees.
 18. The suspension system of claim 16 furthercomprising a first pivot stop and a second pivot stop, said first andsecond pivot stops being operably coupled with said first lift springend and limiting rotation of said first lift spring end to a predefinedangular range.
 19. The suspension system of claim 16 wherein said secondlift spring end is non-pivotally fixed relative to a portion of saidsupport arm assembly.
 20. The suspension system of claim 16 furthercomprising a first pivot stop and a second pivot stop, said first pivotstop being fixed relative to said vehicle chassis and limiting pivotalmovement of said lift spring member in a first rotational direction,said second pivot stop being fixed relative to said vehicle chassis andlimiting pivotal movement of said lift spring member in an oppositesecond rotational direction.
 21. The suspension system of claim 20further comprising a pivot mount secured to said first lift spring end,said pivot mount having a generally U-shaped configuration with a pairof side walls and a central web extending therebetween, said pivot axisextending between said sidewalls and intersecting said sidewalls at asubstantially perpendicular axis, said first and second pivot stopsbeing engageable with said central web on opposite sides of said pivotaxis to thereby limit rotation of said first lift spring end.
 22. Thesuspension system of claim 21 further comprising: a structural memberextending longitudinally from said cross member and having a bushingmounted on a distal end thereof; and a pivot pin extending through saidbushing and said side walls pivotally joining said lift spring memberand said structural member and defining a pivot axis, said pivot axisintersecting a central axis defined by said lift spring member at anangle of approximately 90 degrees.
 23. The suspension system of claim 22wherein said first and second pivot stops are defined by plate membersfixed to said structural member proximate said distal end thereof andlying in a plane oriented substantially perpendicular to said pivotaxis.
 24. The suspension system of claim 16 wherein said support armassembly includes an upper support arm having opposite ends respectivelypivotally connected to a first one of said hangers and said axleassembly; said support arm assembly further including a lower supportarm having opposite ends respectively pivotally connected to said firsthanger and said axle assembly, whereby said upper and lower support armsdefine a parallelogram linkage; said second lift spring end beingnon-pivotally fixed relative to said upper support arm.
 25. Thesuspension system of claim 24 wherein said second lift spring end isnon-pivotally fixed to said upper support arm by a rigid memberextending laterally from said upper support arm.
 26. A lift axlesuspension assembly for a vehicle having a chassis, said lift axlesuspension assembly comprising: an axle assembly; a support arm assemblyoperably coupling said axle assembly to the vehicle chassis wherein saidaxle assembly is vertically moveable relative to the vehicle chassisbetween an uppermost position and a lowermost position; a supportbiasing member operably disposed between said axle assembly and thevehicle chassis; a lift spring member wherein: (a) said lift springmember is an air spring having opposing first and second ends anddefining a central axis; (b) said first end of said lift spring memberis pivotally mounted about a pivot axis; (c) said lift spring member isoperably disposed between the vehicle chassis and said axle assemblywherein extension of said lift spring member vertically displaces saidaxle assembly, said central axis having a first angular positionrelative to said pivot axis when said axle assembly is in said lowermostposition and a second angular position relative to said pivot axis whensaid axle assembly is in said uppermost position, said first and secondangular positions defining a first predefined angular rangetherebetween; and first and second pivot stops disposed proximate saidfirst end of said lift spring member wherein said first pivot stoplimits rotation of said lift spring member in a first rotationaldirection about said pivot axis and said second pivot stop limitsrotation of said lift spring member in a second opposite rotationaldirection about said pivot axis whereby rotation of said lift springmember about said pivot axis is limited to a second predefined angularrange between said first and second pivot stops, said second predefinedangular range being larger than said first predefined angular range. 27.The lift axle suspension of claim 26 wherein said pivot axis is fixedrelative to the vehicle chassis.
 28. The lift axle suspension of claim27 wherein said second end of said lift spring member is non-pivotallyfixed relative to a portion of said support arm assembly.
 29. The liftaxle suspension of claim 26 further comprising a pivot mount secured tosaid first end of said lift spring member, said pivot mount having agenerally U-shaped configuration with a pair of side walls and a centralweb extending therebetween, said pivot axis extending between saidsidewalls and intersecting said sidewalls at a substantiallyperpendicular axis, said first and second pivot stops being engageablewith said central web on opposite sides of said pivot axis to therebylimit rotation of said first end of said lift spring member.
 30. Thelift axle suspension of claim 29 further comprising: a structural memberextending in a direction substantially perpendicular to said pivot axisand having a bushing mounted on a distal end thereof, said bushing beingpositioned concentric with said pivot axis; and a pivot pin extendingthrough said bushing and said side walls pivotally joining said liftspring member and said structural member and defining said pivot axis.31. The suspension system of claim 30 wherein said first and secondpivot stops are defined by plate members fixed to said structural memberproximate said distal end thereof and lying in a plane orientedsubstantially perpendicular to said pivot axis.